Semiconductor substrates are an important part of many microelectronic devices used in computing devices, cell phones, and other electronic equipment. The market for these devices demands increasingly small, intricate, and delicate features. During the manufacturing of these devices, features are created on and below the surface of the substrates. Intermediate manufacturing processes that create the features often leave residual particles or other contaminants on substrate and feature surfaces, such as liquid-borne contaminants or reactor chamber particles commonly encountered in semiconductor manufacturing. Because feature dimensions now approach the size of the residual particles and aspect ratios are increasing, the particles can substantially fit into small grooves or other negative spaces of features. This makes it difficult to remove the residual particles. Additionally, very small features are fragile and therefore susceptible to damage from the cavitational and/or other kinetic forces of conventional cleaning techniques. As such, there is a need in the art for a cleaning system and process that sufficiently removes residual particles from the surface of a substrate without unacceptably damaging the substrate features.
FIGS. 1-3 illustrate examples of existing methods of removing residue and particles from a substrate surface. One disadvantage of these methods is that the energy levels at the substrate surface required to adequately remove a sufficient quantity of particles may damage the features at the substrate surface. FIG. 1 illustrates a nano-spray method in which a nozzle 110 is positioned above a substrate 120 in a gas-ambient environment 130 (e.g., air, nitrogen, etc.). A spray 140 is directed from the nozzle 110 onto a surface of the substrate 120. The spray 140 can comprise either an atomized spray (containing incompressible and compressible fluids) or a fluid spray (incompressible fluid only). Nano-spray methods remove more particles as the force of the spray increases, and successful cleaning of particles from small features often requires energy above a damage threshold for many types of small surface features.
FIG. 2 depicts an existing mega-sonic cleaning method in which a substrate 120 is held within a chamber 150 by a chuck 160. The substrate 120 is immersed in a fluid 170 within the chamber 150, and a transducer 180 emits megasonic energy 190 at a high frequency to remove particles and residue from a surface of the substrate 120. This method causes cavitation at the surface of the substrate to dislodge the residual particles, but the cavitational forces can damage features on the surface depending on the megasonic energy level. The existing methods shown in FIGS. 1 and 2 are difficult to control because they create a fluid amalgam of compressible fluids and incompressible fluids on the surface of the substrate.
FIG. 3 shows a simplified depiction of the compressible and incompressible fluid amalgam 126 that occurs with conventional techniques. A nozzle 110 represents a conventional nozzle for use with nano-spray, Ocean-spray, M-jet, N-jet, or similar techniques. The nozzle 110 delivers a spray 140 onto the substrate 120 through air, an inert gas, or another type of compressible fluid medium 130. The substrate 120 contains features 122 that project upwardly from and/or recede below the surface of the substrate 120. (It is to be appreciated that the dimensions are not necessarily to scale.) Some features may extend above the surface 127 of the accumulated amalgam 126. As the spray strikes the surface of the substrate 120, the turbulence in the spray causes the incompressible fluid of the spray 140 to mix with the compressible ambient fluid 130. This mix 124 has highly varying pressure zones throughout. The mix 124 causes compressible fluid to accumulate in the amalgam 126 and congregate at regions of the surface of the substrate 120. This can cause an unpredictable and adverse pressure differential between regions that contact the amalgam mix 128 and those that do not 129. A similar amalgam mix occurs through cavitation caused by other, non-spray techniques such as mega-sonic cleaning techniques.
Another cleaning method (not shown) uses a bulk flow of fluid across a surface of a substrate in order to remove particles from the surface features of the substrate. The fluid boundary layer at the surface of the substrate in such a fluid flow is generally much larger than the height of the features; as a result, the flow velocity at the level of the features is too low to substantially assist in particulate removal. Despite changing variables such as flow velocity and fluid properties, it is difficult or impossible to reduce the boundary layer to effectively remove particles from the substrate surface. As such, the small size of the surface features and of the residue particles renders this method ineffective.
In summary, conventional cleaning methods may not satisfactorily provide effective cleaning at the substrate surface without damaging the very small surface features in current high-density dies. Moreover, existing nano-spray and megasonic methods generally require a compromise between the desired degree of particle removal and the acceptable amount of feature damage. In light of the existing cleaning techniques, there is a need for a cleaning method that can successfully remove particles and residue from a substrate surface without damaging the features.